In the sheet feed device for supplying sheets to the image forming position of the image forming apparatus, a technique has been developed to float the loaded sheet by blowing air thereto in order to ensure stable sheet feed independently of the properties and size of the sheet.
In a proposal disclosed in the Japanese Patent Application Publication No. 2006-264980 and Japanese Patent Application Publication No. 2010-137963, a sensor is used to detect the sheet floated by air. Based on the result of detection, the volume of air blown to the loaded sheet is controlled to provide a stable sheet feed.
In the Japanese Patent Application Publication No. 2008-87906, to ensure stable feed of various types of sheets different in sheet size, basis weight and surface roughness, air is blown close to the trailing edge of loaded sheets in the traveling direction.
In recent years, an image forming apparatus using electrophotographic process has come to be employed in the field of printing. A great advantage of omitting a plate making process is provided if the image forming apparatus using electrophotographic process is used in printing. To put it more specifically, when the image forming apparatus using electrophotographic process is used in printing, sheets can each be printed with different patterns. As a result, the image forming apparatus is used as a printing machine for printing an address on an envelope.
When an address is printed on the envelope, an envelope is used as a sheet. The envelope is not a regular printing sheet or a flat sheet. It is folded in two or three, and some parts are bonded. The process of feeding the envelope to the image forming section faces a new problem not found in the flat sheet.
The Japanese Patent Application Publication No. 2006-264980, No. 2010-137963 and No. 2008-87906 are intended to ensure stable sheet supply, but not to solve problems in feeding the envelope.
The object of the present invention is to provide a sheet feed device and image forming apparatus equipped therewith, wherein loaded envelopes are separated one by one and are supplied in a stable manner.